Regrettably, more than 29,000 fatalities, 2.2M injuries, and $100 Billion dollars in financial losses occur annually on United States roads alone. There has been shared consensus among researchers and governments that those figures can be brought down by applying modern safety applications. The evolving technologies promise to make transportation safer than ever by embedding electronic safety features powered by wireless sensing in vehicles and roads. Location based features are at the heart of this evolution. In particular, identifying the exact position of a moving vehicle (object) is a key aspect to developing most of the vehicular safety features and commercial Location-Based-Applications (LBA).
Global Navigation Satellite Systems (GNSS) such as Geographical Positioning Systems (GPS) have been used for positioning objects with reasonable accuracy. GPS provides typically less than 70 cm accuracy and there have been several studies showing that GPS cannot be efficiently used in urban environment due to dilution of precision and the urban canyon phenomenon. Most safety applications require sub centimeter accuracy with high reliability in urban and sub-urban environments.
Undoubtedly, GPS is the most popular GNSS technology used for positioning objects up-to a normal accuracy of a few meters by timing the transmitted signal along a line-of-sight (LoS) between the satellite and the mobile earth object. If no clear LoS is available between the satellite and the mobile object, ranging to that satellite becomes impossible. The popularity of GPS led to increased interest in Location Based Systems (LBS) where applications behave differently based on user position. Serious and high-end LBS systems such as safety and mission-critical applications cannot tolerate limited positioning accuracy, limited signal availability in urban environment, cloudy/bad weather, or the lack of integrity indicators.
Accurate GNSS positioning (error <30 cm) requires the availability of multiple satellite signals (5+) which is impossible in urban and metropolitan areas. The transportation industry has an inevitable and imperative need to resolve the problem of inaccurate positioning in order to unlock the essential development of safety and automation applications. Unfortunately, GNSS and GPS systems exhibit the following inherent distinctive limitations:
a) Limited signal availability in urban environments, cloudy skies, or tunnels.
b) Insufficient accuracy to serve serious and high-end LBS systems like safety and mission-critical application.
c) Loss of precision until Time-To-First-Fix (TTFF) is made available. The TTFF is the time required for the receiver to acquire ephemeris as well as an almanac for all satellites that contains coarse orbit and status information for each satellite in the constellation. Fix times are unacceptably long, and fixes may never be reached when attenuation levels exceed 30 dB, which is likely in an urban environment and in bad weather.
d) Limited redundancy since GPS has no alternative system to be used in its absence.
e) Satellite-based systems are too centralized and lack the desired localized control.
Accordingly, there is a need for an accurate positioning system and method that provides improved positioning accuracy in a mobile environment.
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.